1. Field of the Invention
The present invention relates generally to tubular sheaths, and more particularly to tubular sheaths used for permitting percutaneus introduction of devices, e.g., a catheter, or the like, into a patient.
2. Background
Introducer sheaths are commonly used by medical personnel for permitting percutaneus insertion of devices such as catheters, or the like, into patients. Introducer sheaths advantageously allow medical personnel to insert such devices into vascular systems of patients without requiring invasive surgical procedures, thereby facilitating the use of such devices and minimizing the recovery time of the patient.
Various design configurations and processes for manufacturing have been used in the production of sheaths for medical applications. For example, in U.S. Pat. No. 4,306,562 (the ""562 patent) issued Dec. 22, 1981, to Osborne, a flexible cannula is disclosed. In accordance with that disclosure, the flexible cannula comprises material which tears readily in a longitudinal direction and can thus be easily removed by pulling tabs on opposite sides of the cannula apart after the catheter or other device has been inserted into the body. The ""562 patent further discloses that the cannula is disposed about a dilator having a distal end that is tapered for enlarging a puncture site to accommodate the cannula. Similarly, the cannula has a distal end where there is a slight taper to create an appropriately snug fit with the dilator and also to facilitate the enlarging of the puncture site to accommodate the cannula.
Moreover, the ""562 patent discloses that the tapered distal end of the cannula is formed by measuring an appropriate length of tubing; applying a heat gun to the tubing; and, upon application of this heat, stretching the tubing, thereby yielding the tapered end. The tip is then cut at a point where the inside diameter of the cannula approximates the outside diameter of the dilator, which will be used with the particular cannula. The ""562 patent discloses that the heat-formed tapered end of the cannula serves two purposes. First, it facilitates insertion of the cannula into the body. Second, a tight fit with a probe at this end minimizes blood loss.
In addition, in U.S. Pat. No. 4,581,025 (the ""025 patent) issued Apr. 8, 1986, to Timmermans, a sheath is disclosed. In accordance with that disclosure, the sheath comprises a tubular structure formed of a flexible material that is compatible for insertion within the body and having proximal and distal ends. In one embodiment, the tubular structure includes one slit having an open and a closed end. The tubular structure is further comprised of a tab defined by the slit, whereby when the tab is pulled apart from any object extending through the lumen of the tubular structure, the tubular structure tears longitudinally removing the tubular structure from the object. In another embodiment, the tubular structure is cuffed between the closed end of the slit and the distal end of the tubular structure, the cuff defining the proximal end of the tubular structure. The cuff prevents the slit from tearing prematurely and further provides a blunt, smooth open end at the proximal end that permits closure thereof by thumb pressure only in order to temporarily block blood flow or air aspiration during use. The ""025 patent further discloses that the distal portion of the sheath is provided with a rounded or tapered tip to ensure a desirably snug fit between a dilator and the sheath and facilitate smooth introduction of the sheath within the body.
Introducer sheaths have traditionally been made of thermoplastic materials, and various processes for manufacturing have been used with such thermoplastic materials. For example, in U.S. Pat. No. 5,139,407 (the ""407 patent) issued Aug. 18, 1992, to Kim et al., an apparatus for reducing thermoplastic material compression mold cycle time is disclosed. In accordance with that disclosure, a thermoplastic sheet is placed between a pair of mold members each having a thermal insulator and a mating metal mold insert. Radio frequency (RF) energy is applied to the inserts to dielectrically heat and melt the thermoplastic sheet. The heated sheet is then deformed in a low-pressure press with the insulators. The insulators are then replaced with cool thermally conductive structures to shorten the cooling cycle time. The thermally conductive structures cool the sheet by pressing the sheet in a high-pressure press. The ""407 patent further discloses that such thermoplastic materials include TEFLON(trademark) polytetrafluoroethylene (PTFE), which is sold by and a trademark of the E.I. DuPont Co., Inc., Wilmington, Del., USA.
In addition, in U.S. Pat. No. 5,360,330 (the ""330 patent) issued Nov. 1, 1994, a RF heated mold for thermoplastic materials is disclosed. In accordance with that disclosure, a source of RF energy is applied to a low thermal inertia heating element with high thermal conductivity, such as a spool, for rapidly heating the heating element to settable predetermined temperature, which temperature is maintained essentially constant. The heating element is detachably attached about the die of a mold for transferring heat to the die to form, mold, weld, or extrude thermoplastic material placed within the mold. Thermal chokes restrict heat transfer from the die to the remainder of the mold. One or more heat sinks draws and dissipates heat from the thermal chokes to maintain cool zones of the mold. Following the heating cycle, upon termination of application of RF energy to the spool, cooling may be accelerated by directing a stream of gas upon the heating element. The ""330 patent further discloses a mold for the purpose of tapering an end of a thermoplastic sleeve, which is subsequently disposed about an intravenous catheter and is used for engaging the catheter with a vein of a patient. The tapered end of the thermoplastic sleeve facilitates sliding insertion of the end portion of the sleeve into the vein of the patient.
Although the various design configurations and manufacturing processes described above have been used in the production of introducer sheaths, we have recognized that forming tapered tips at the ends of introducer sheaths continues to be problematic, especially when introducer sheaths are made using preferred PTFE thermoplastic materials such as TEFLON(trademark) PTFE. This is because PTFE thermoplastic materials generally have very high melting temperatures. Further, certain radiopaque substances, which are commonly added to the thermoplastic materials for facilitating x-ray or fluoroscopic visualization of the introducer sheaths, frequently cause discoloration of the introducer sheaths when the tapered tips are formed using heat or RF energy. As a result, processes for forming tapered tips of introducer sheaths that involve either heat or RF energy are often difficult to implement.
As an alternative to using heat or RF energy, tips of introducer sheaths may be tapered using a grinding process. However, introducer sheaths with formed tapered tips are generally regarded as being superior to introducer sheaths with ground tapered tips because the inner diameter of a formed tapered tip typically decreases around a forming mandrel, thereby resulting in an interference fit between the introducer sheath and a dilator disposed therein. This is advantageous when using the introducer sheath during the insertion of devices, e.g., a catheter, or the like, into a patient because there is essentially no gap between the sheath and the dilator that might get hung-up when the sheath and the dilator in combination penetrate the patient""s skin or arterial/venous wall.
In contrast, because the inner diameter of a ground tapered tip typically does not decrease during the grinding process, it is very difficult to obtain a useful interference fit between an introducer sheath with a ground tip and a dilator disposed therein. This means that there is often a gap between the ground tip and the dilator that can get hung-up when penetrating the patient""s skin or arterial/venous wall, thereby making the insertion of the introducer sheath into the patient unsuccessful.
Specifically, when an edge of the introducer sheath gets hung-up when penetrating the patient""s skin or arterial/venous wall, a condition commonly known as xe2x80x9cpeel-backxe2x80x9d frequently occurs. For example, during peel-back, the tapered tip of the introducer sheath typically distorts into an accordion-shape, thereby making sheath insertion virtually impossible. As a result, the distorted sheath/dilator set must be discarded, and another attempt must be made using a new sheath/dilator set. Not only is there a risk of potentially harming the patient""s dermal and vascular systems during peel-back, but having to discard distorted sheath/dilator sets also substantially increases costs.
In addition, we have recognized that making an introducer sheath that is easily torn longitudinally, i.e., peelable, for removing the sheath from a device disposed therein is also problematic. For example, a conventional method for making a peelable introducer sheath includes mechanically skiving two (2) score lines on the outer surface of the introducer sheath, approximately 180xc2x0 apart, that run longitudinally the entire length of the sheath. As a result, when the introducer sheath is split and peeled, the sheath tears in half along the two (2) score lines.
However, there are several variables that are known to affect the consistency and reliability of peelable introducer sheaths that are made according to this conventional method. For example, at the beginning of a production run, blades used to skive the outer surface of the introducer sheath are typically very sharp, but gradually become dull during the course of the production run. Such blade wear generally affects the quality of the score lines and therefore the consistency and reliability of the peel. Further, the blades are typically designed to cut to a predetermined depth. But, if, e.g., the wall thickness, the outer diameter, and/or the inner diameter of the sheath changes during the production run, then the cut depth may also change, thereby affecting the consistency and reliability of the peel.
It would therefore be desirable to have an introducer sheath with a formed tapered tip that is easy to manufacture and inexpensive to use. Such an introducer sheath would be made of preferred PTFE thermoplastic materials such as TEFLON(trademark) PTFE. It would also be desirable to have an introducer sheath with a formed tapered tip that can be torn longitudinally, i.e., peelable, for easily removing the sheath from any device disposed therein.
The present invention provides a peelable introducer sheath with a formed tapered tip that is easy to manufacture and inexpensive to use. Specifically, manufacturing methods disclosed herein allow the production of introducer sheaths with thermally formed tapered tips that have no visible discoloration due to the thermal tip-forming process. Further, the introducer sheaths with formed tapered tips are externally visible during use by x-ray or fluoroscopic techniques. Still further, the introducer sheaths manufactured in accordance with the present invention allow straight and even peeling along the full length of the introducer sheaths.
According to one embodiment of the present invention, a method of manufacturing a multi-layer sheath, comprising the steps of preparing a first composition blend for forming an inner layer of the multi-layer sheath; preparing a second composition blend for forming an outermost layer of the multi-layer sheath; combining the first and the second composition blends into a multi-layer pre-form; processing the multi-layer pre-form for producing coherent tubing; and, forming a tip at one end of the coherent tubing using a thermal process, thereby producing the multi-layer sheath having the inner layer, the outermost layer, and the formed tip, wherein the method includes the substep of adding a detectable material to the first composition blend for facilitating external visualization of the multi-layer sheath.
According to another embodiment of the present invention, a method of manufacturing a multi-layer sheath, comprising the steps of preparing a first composition blend for forming an inner layer of the multi-layer sheath, including the substep of adding a detectable material to the first composition blend for facilitating external visualization of the multi-layer sheath; preparing a second composition blend for forming an outermost layer of the multi-layer sheath; combining the first and the second composition blends into a multi-layer pre-form; processing the multi-layer pre-form for producing coherent tubing, wherein the processing includes the substep of performing a reduced sintering process; and, forming a tip at one end of the coherent tubing using a thermal process, thereby producing the multi-layer sheath having the inner layer, the outermost layer, and the formed tip.
Still further aspects and advantages will become apparent from a consideration of the ensuing description and drawings.